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 A089757 Distinct multiples of 3 such that the concatenation of a(n), a(n-1), ..., a(2), a(1), 1 is a prime and a(n) > a(n-1). 1

%I

%S 3,6,9,12,27,30,39,42,66,162,231,252,258,273,276,411,474,531,543,642,

%T 699,732,795,819,1023,1059,1101,1257,1281,1842,1872,1902,1953,2028,

%U 2076,2223,2331,2922,3063,3102,3414,3522,3624,3714,3867,4320,4383,4482,4788

%N Distinct multiples of 3 such that the concatenation of a(n), a(n-1), ..., a(2), a(1), 1 is a prime and a(n) > a(n-1).

%e 31, 631, 9631, 129631, etc. are primes.

%e a(10) = 231 because 2311626642393027129631 is prime.

%p ds:=proc(s) local j: RETURN(add(s[j]*10^(j-1),j=1..nops(s))): end: a:=[]: k1:=1: for n from 1 to 50 do for k from k1 do m:=ds([1,seq(op(convert(a[i],base,10)),i=1..nops(a)),op(convert(3*k,base,10))]): if isprime(m) then k1:=k+1: a:=[op(a),3*k]: break fi od od: op(a); # C. Ronaldo

%Y Cf. A089758.

%K base,nonn

%O 0,1

%A _Amarnath Murthy_, Nov 22 2003

%E More terms from _Jim Nastos_, Jan 31 2004

%E More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 26 2004

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Last modified September 21 14:10 EDT 2021. Contains 347598 sequences. (Running on oeis4.)